1. Field of the Invention
The present invention relates to a coupling mechanism between an optical subassembly and a circuit board, in particular, a coupling mechanism using a flexible printed circuit board.
2. Related Prior Art
Conventional coupling mechanism between an optical subassembly (hereinafter denoted as OSA) and a circuit board with a flexible printed circuit board (hereinafter denoted as FPC board) is, for example, one end portion of the FPC board is inserted with lead pins of the OSA and the FPC board thus assembled with the OSA is connected to a primary surface of the circuit board by bending the FPC board between the OSA and the circuit board. Such mechanism has been disclosed in a Japanese Patent application published as JP-H11-345987A.
However, this conventional mechanism has various subjects to be solved. That is:
(1) The FPC board is necessary to extend to be bent, which influences the high frequency performance of the transceiver that installs the OSA and the circuit board;
(2) Although a gap between the OSA and the circuit board may be adjusted by bending the FPC board to align the OSA along an optical axis thereof, mechanical stress is induced at the contact point of the FPC board with the circuit board, which causes a break of wiring pattern on the FPC board;
(3) Electrical connection between the OSA and the circuit board is realized by inserting the lead pins of the OSA into via holes provided in the FPC board and by soldering thereafter. However, the space between lead pins becomes smaller as the transceiver miniaturizes, which makes it hard to insert lead pins into the holes and to solder them. For example, assuming the diameter of the OSA is 3.8 mm and has four lead pins, the space therebetween becomes 0.45 mm. Moreover, for the side of the circuit board, the space between via holes into which the lead pin is inserted therein is only left by 0.5 mm, assuming the diameter of holes is 0.45 mm. The FPC board applicable to such small spaced lead pins is hard not only to manufacture it but also to solder them.
(4) A functional OSA requires a number of lead pins. One type of such numerous lead pins is known as an arrayed lead pin, in which the pitch of lead pins becomes further smaller as compared to those mentioned above. In order to solder or to connect this arrayed lead pins to the FPC board, respective pins is necessary to be expanded in their interval at a distal end, which makes it complex and costly to manufacture the transceiver.